Effect of double abutment absorption of alveolar bone in rigid fixed bridge on the stress distribution of abutments

目的:探讨固定桥双基牙侧牙槽骨有不同程度水平吸收时,基牙牙周膜的等效应力值和分布的变化,以指导临床固定桥的合理设计。方法:采用螺旋CT扫描技术与MIMICS、AnSyS软件相结合建立双基牙侧牙槽骨有不同程度水平吸收后的三基牙双端固定桥的三维有限元模型,施加垂直和斜向45°载荷,分析双基牙侧牙周膜的应力分布状况。结果:1斜向载荷下各模型应力值均大于垂直向载荷时的应力,应力集中现象也较垂直向载荷时明显;2在垂直或倾斜载荷下,有牙槽骨吸收的第二前磨牙侧增加牙周组织健康的第一前磨牙时,应力均变大以分担牙合力;若增加的第一前磨牙有不同程度的牙槽骨吸收,垂直载荷时应力值变化不大,斜向载荷时应力值减小,但应力集中现象较无吸收时明显。结论:增加牙槽骨有不同程度吸收的基牙不能有效地发挥分散牙合力的作用,不适合做固定桥基牙。加载方向是影响应力分布的重要因素,应注意防止产生过大的侧向力。AIM: To investigate the stress distribution of abutment tooth periodontal ligament when there are different levels of alveolar bone resorption at the abutment teeth with rigid fixed bridge design.METHODS: A three dimensional finite element model with different levels of alveolar horizontal absorption at the abutment teeth was established by CT scanning using Mimics 8.1 and Ansys 11.0.Vertical and oblique loading was added to test stress the distribution at the abutment teeth.RESULTS: When the periodontally healthy first premolar was added as additional abutment tooth,vertical loading and oblique loading could result in more evenly distributed stress.However,when alveolar bone resorption existed in first premolar,little stress distribution change was observed at vertical loading.But oblique loading led to more concentrated stress.CONCLUSION: Adding an abutment tooth with alveolar bone resorption can not improve stress distribution,hence it is not suitable for rigid fixed bridge.The direction of loading seems to play a significant role in determining stress distribution.The oblique force on the bridge should be avoided or reduced as possible.厦门市科技局资助课题(3502Z20094013

兰州重离子加速器的新低温泵

本文介绍了兰州重离子加速器新型大口径无液氮低温泵——HIRFL800。它是由一台改良的小型单级机械制冷机和一台标准的二级制冷机组成的。泵对氮和氢的抽速分别为24000和26000 L/s。自1989年以来,用八台HIRFL低温泵,在100 m~3大真空室上,获得了5×10~(-6)Pa的真空度

滑坡变形破坏的三维SPH模拟方法研究

建立了一套基于SPH计算框架的三维土体大变形模型,采用了非关联流动法则下的Drucker-Prager土体本构来描述土体破坏的发生、发展到最终稳定的全过程

Simulation of the Motion of a Bead in Shallow Water via SPH Method

This paper numerically investigated the two-dimensional motion of a bead in shallow water down a steep rough bed via smoothed particle hydrodynamics (SPH). The motivation of this work is to study the mechanism of particle transport in shallow flows. The simulated results show agreement with the experimental data which also verifies the validity of SPH. Moreover, a series of numerical experiments are carried out to discuss the influences of bead material, slope gradient on the characteristics of bead motion and the state of shallow flow

research on modeling and simulation of satellites surface optical reflection characteristics

在研究空间相机成像效果探测问题时,针对提高探测相机成像真实效果的需要,研究了卫星表面光学反射特性的建模与仿真方法。利用双向反射分布函数(BRDF)仿真卫星表面的光学反射特性,将卫星表面物理特性与其光学反射特性有机地结合起来。在VC.Net环境下开发卫星表面光学反射特性仿真软件,并将软件集成到空间探测相机成像效果仿真平台上。利用平台进行成像仿真实验,生成真实感仿真图片。仿真结果表明,BRDF能够精确仿真卫星表面的光学反射特性,使成像效果仿真更加准确和逼真

Construction of a three-dimensional finite element model of the absorbed alveolar bone of fixed partial denture abutments

目的:通过建立左侧下颌后牙5单位固定桥双基牙侧牙槽骨吸收的有限元模型,为分析双基牙侧牙槽骨吸收对牙周膜应力的影响打下基础。方法:采用多层螺旋CT扫描技术与MIMICS、AnSyS软件相结合对88张层厚为0.6MM的CT断层影像进行三维重建,在此基础上建立双基牙侧牙槽骨吸收模型。结果:建立了5单位固定桥有限元模型及双基牙侧牙槽骨吸收的有限元模型,包括牙齿、牙周膜、牙槽骨。结论:所建模型结构完整,单元划分精细,能够较精确地模拟牙槽骨吸收的实体状态,为加载后的基牙牙周膜应力分析提供基础。ADM:To construct three-dimensional finite element models(FEMs) of five-unit fixed partial denture of left mandible so as to analyze the effects of double abutments alveolar bone resorption on periodontal ligament stress.METHODS:Eighty-eight CT slice pictures(0.6mm in thickness) were treated with multislice helical computed tomography scanning technology,Mimics and Ansys Software to build the FEMs.Then the alveolar bone of double abutments inordinately absorbed models on the basis of the FEMs was built.RESULTS:A three-dimensional FEMs of five - unit fixed partial denture and alveolar bone resorption of double abutments model were constructed,including teeth,periodontal ligaments and alveolar bone.CONCLUSION:The constructed models had the advantages of intact structure,precise elements and can simulate the natural situation of alveolar bone resorbtion and can provide basis for further research of periodontal ligament stress induced by loading.厦门市科技局基金资助项目(3502Z20094013

中国科学院力学研究所流固耦合系统力学重点实验室;

土坝漫项溃决过程中溃口冲刷到一定程度将会引起坝体边坡失稳破坏。土体大变形和裂缝的三维扩展是边坡变形破坏的典型特征。有限元等网格类方法在处理这类问题时往往需要进行复杂的网格处理,常常不能精确地模拟裂缝间断和土体的塑性流动。因此,部分学者开始尝试使用无网格类方法来模拟边坡失稳过程,并且取得了不错的成果。但是这些研究多局限于二维平面问题,忽略了实际边坡的三维效应。另外,这些研究多侧重于方法的实现,缺乏对边坡破坏特征的讨论及对其中规律的探讨。作为一种典型的拉格朗日型无网格粒子法,SPH(Smoothed particle hydrodynamics)方法在处理大变形和界面流动问题时具有明显的优势。因此..

海底滑坡变形破坏的水土耦合数值模拟研究

使用岩土弹塑性本构描述土体应力变形,使用N-S方程描述水体运动,通过水土粒子直接传递力的方式描述水土相互作用,在避免了网格类方法的网格重构或自由面追踪等问题的同时,实现了水体和上体的强耦合过程.基于所发展的水土强耦合数值模型,对典型的海底滑坡问题进行了模拟分析,讨论了不同坡度、不同土体c、不同水深等参数条件下所产生的滑坡体形态演化规律